1. Field of the Invention
This invention relates to an improved process for the absorption of acid gas from a feed gas using an aqueous alkaline solution. More particularly, it relates to a method for reducing undesirable foaming of an aqueous alkaline acidgas absorption solution.
2. Prior Art
The removal of acid gases, principally carbon dioxide and hydrogen sulfide, from gas streams is of considerable industrial importance. Frequently the removal is accomplished by contacting the gas stream with an aqueous alkaline solution and absorbing the acid gas into the solution, stripping the absorbed gas from the solution and regenerating the solution in a separate stage. The thus-regenerated solution is then recycled to the absorption stage. The method is effective, yet not without difficulties. For example, aqueous alkaline solutions have a natural inclination to foam, and the passing of a gas into a foamable solution is classic to the production of a foam. Consequently, resort to the use of anti-foaming agents as additives to the aqueous solution is common practice in the art, as may be noted from U.S. Pat. No. 2,544,564, for example. Nevertheless, excessive foaming, that is foaming in excess of that ordinarily accommodated by the method, is not uncommon. In this event, the excess foaming poses a severe limitation upon the process in that gas flow rates must be substantially reduced to keep the foaming within tolerable limits. In the extreme, the excessive foaming may be akin to a process disaster in that even with a reduction in gas flow a seemingly inexorable flow of foam filling the absorption zone and overflowing into downstream process lines is experienced. The cause of this more-or-less unbridleable foaming appears to be manifold and attributable to not one, but a variety of factors, including compressor lubricating oil condensate, the presence of excess anti-foam agent, and hydrocarbon condensate from the processed gas stream, especially where the source of the gas stream is a petroleum recovery or process stream, and the like. These factors act singly and/or in concert upon the action in the gas absorption and stripping zone. The substantial reduction and/or control of excessive foaming in an acid-gas absorption process is an object of the present invention.